Photoinduced Ullmann C-N coupling: demonstrating the viability of a radical pathway.

Carbon-nitrogen (C-N) bond-forming reactions of amines with aryl halides to generate arylamines (anilines), mediated by a stoichiometric copper reagent at elevated temperature (>180°C), were first described by Ullmann in 1903. In the intervening century, this and related C-N bond-forming processes have emerged as powerful tools for organic synthesis. Here, we report that Ullmann C-N coupling can be photoinduced by using a stoichiometric or a catalytic amount of copper, which enables the reaction to proceed under unusually mild conditions (room temperature or even -40°C). An array of data are consistent with a single-electron transfer mechanism, representing the most substantial experimental support to date for the viability of this pathway for Ullmann C-N couplings.